Epoxy resin compositions are thermosetting resin compositions that are used in a wide range of fields including electrical and electronic parts, structural materials, adhesives and coating materials, because of their manageability and the excellent electrical characteristics, heat resistance, adhesion and humidity resistance (water resistance) of their cured products.
Sealing materials are used in electronic devices to protect the electronic parts such as semiconductor elements from factors in the external environment including impacts, pressure, humidity and heat. Such sealing materials have epoxy resins as the active compounds, and epoxy/phenol-based sealing materials with phenol resin curing agents are widely used.
Power semiconductors, such as on-vehicle power modules, are electronic devices considered to be an important key technology for achieving energy savings in electrical and electronic devices, and there is an increasing trend toward silicon carbide (SiC), gallium nitride (GaN) and diamond (C) semiconductors, known as wide band gap semiconductors, that promise higher current, smaller sizes and greater efficiency for power semiconductors, as well as higher efficiency than conventional silicon (Si) semiconductors. The advantage of SiC semiconductors is their ability to operate under higher temperature conditions, and therefore semiconductor sealing materials must have even higher heat resistance than currently exhibited.
In the case of power semiconductors with high voltage resistance specifications, the working voltage may reach from several hundred to several thousand volts. Under such high voltage conditions, defects have been reported to occur due to the phenomenon of partial discharge. Partial discharge is the phenomenon in which local discharge between an electrode and an insulator surface (surface corona) or discharge in the gap (void) inside an insulator (void corona) causes corrosion of the insulator.
With a crosslinkable polymer, higher crosslink density prevents breakdown caused by electric field-accelerated electrons and helps minimize formation of fine pores, potentially improving the insulating property. Minimizing formation of fine pores in the cured product in the steps of resin molding such as transfer molding is also thought to improve the insulating property.
Materials reported to have excellent heat resistance include heat-resistant resin compositions comprising maleimide compounds and polyamines (see PATENT DOCUMENT 1), and bismaleimide resins modified with polybenzoxazine (see PATENT DOCUMENT 2). Such heat-resistant resin compositions, when cured, can exhibit excellent heat resistance.